For part-time employees the gap is -2.0%, compared to -3.7% in 2008, and the gender pay gap for all employees has fallen to 22.0% from 22.5% in 2008.

But while the public sector saw a decrease in the gender pay difference to 21.0% from 22.0% in 2008, the private sector pay gap widened by 0.7 percentage points to 28.8%, up from 28.1% the previous year.

Harriet Harman, minister for women and equality, welcomed the narrowing of the overall pay gap but said it was disappointing to see the private sector lagging behind the public sector.

She said: “Most women work part-time because they juggle the important work of looking after children and older relatives: that’s where the discrimination really bites. It’s women working part-time who get clobbered with unequal pay.

“The gender pay gap has fallen by more than 5% since 1997. Today’s figures are a small step in the right direction and the Equality Bill will help make even further progress by shining a spotlight on gender pay discrimination, workplace by workplace, so problems can be identified and action taken. Employers will no longer be able to rely on keeping their pay structure secret.”

Stephen Overell, associate director of The Work Foundation, said: “There is clear evidence of demonstrable progress here in which legal, organisation and cultural factors have all played a part.”